This invention relates to a robot used in clean rooms in order to transport semiconductor wafers contained in a wafer cassette and to load and unload the same automatically to and from semiconductor processing apparatuses.
In the fabrication process of semiconductor devices such as VLSIs and ICs, the occurrence of dust in workrooms is a serious obstruction to the desired high yield of semiconductor devices. That is, the yield of the semiconductor devices is severely influenced by the cleanliness of the workroom's atmosphere. Therefore, semiconductor devices are, generally, processed in clean rooms having a cleanliness level (i.e., the number of dust particles contained in a unit volume of atmosphere) lower than a predetermined level.
In order to eliminate dust completely from a clean room, it is preferred to automate as many processing apparatuses and transfer systems in the clean room as possible. For this reason, several kinds of transporting robots for conveying semiconductor wafers have been used in clean rooms so far. One of these conventional robots has a robot body transferrable along a guide rail disposed in the clean room (K. Satoh, Reduction of Labor and Automation, June issue, p. 43 to 47 (1985)). The robot body includes a clamping hand, the position of which is adapted to be controlled by arm assemblies. This robot can releasably clamp a wafer-encasing cassette with a pair of fingers of the clamping hand and can transport the cassette to a desired place. However, with the above-mentioned conventional robot, manual handling of the cassette is necessary in order to load the cassette into a semiconductor processing apparatus when the processing apparatus requires the cassette to be oriented in a specific direction substantially different from the direction in which the cassette faces during its transportation.